There are known a number of plasma treating apparatus in which a microwave is used as the excitation source for generating plasma. Specific examples of such plasma apparatus are CVD apparatus, etching apparatus, and the like.
The formation of a deposited film using a so-called microwave plasma CVD apparatus is conducted, for example, in such a manner as will be described in the following. That is, a film-forming raw material gas is introduced into the film-forming chamber of the microwave plasma CVD apparatus, and at the same time, a microwave energy is introduced thereinto, whereby the film-forming raw material gas is excited and decomposed with the action of the microwave energy to produce plasma, resulting in causing the formation of a deposited film on a substrate placed in the film-forming chamber.
The etching treatment of a substrate to be treated using a so-called microwave plasma etching apparatus is conducted, for example, in such a manner as will be described in the following. That is, an etching raw material gas is introduced into the treating chamber of the microwave plasma etching apparatus, and at the same time, a microwave energy is introduced thereinto, whereby the etching raw material gas is excited and decomposed with the action of the microwave energy to produce plasma, resulting in etching the surface of said substrate with the plasma in the treating chamber.
In each of these microwave plasma treating apparatus, a microwave is used as the excitation source for the raw material gas used, and because of this, it is possible to chain-like accelerate and excite electrons generated as a result of ionizing the molecules of the raw material gas by an electric field with an extremely large frequency. In this respect, the microwave plasma treating apparatus has advantages such that a high excitation efficiency and a high decomposition efficiency can be attained as for the raw material gas, plasma with a high density can be relatively easily produced, and the plasma treatment of an object can be conducted at a high speed. In addition, there are further advantages in that the microwave plasma treating apparatus can be designed to be of a non-electrode discharging type because the microwave used has a property of transmitting through a dielectric material and in that case, the plasma treatment of an object can be conducted in a highly clean atmosphere.
The introduction of a microwave into these microwave plasma treating apparatus is usually conducted by one of the following three manners. That is, (i) a manner of introducing a microwave transmitted through a waveguide from a microwave power source into the plasma treating chamber through a coaxial antenna, (ii) a manner of introducing a microwave transmitted through a waveguide from a microwave power source into the plasma treating chamber through a dielectric window, and (iii) a manner of introducing a microwave transmitted through a waveguide from a microwave power source into the plasma treating chamber through one or more slots (that is, one or more apertures) disposed at said waveguide. There are known a number of plasma treating apparatus for subjecting an object to plasma treatment, in which these microwave introducing manners are employed.
As an example of the apparatus in which the above manner (i) is employed, there can be mentioned a plasma treating apparatus of the constitution in which a microwave is introduced into a plasma generation chamber through a coaxial antenna which is described, for example, in Japanese Laid-open patent application No. 131175/1980. The plasma treating apparatus described in this publication is of the constitution schematically shown in FIG. 10. The plasma treating apparatus shown in FIG. 10 comprises a vacuum vessel 2105 having an electrically insulative cylinder 2116 installed therein, said insulative cylinder 2116 having a plurality of specimens 2117 spacedly arranged on the inner wall face thereof. A microwave outputted by a microwave oscillation source 2101 is introduced into the vacuum vessel 2105 through a waveguide 2102 and an antenna 2121 made of a metal. When the microwave is introduced into the vacuum vessel 2105, plasma 2125 is produced between a cylindrical body 2122 made of a quartz and the insulative cylinder 2116, wherein the specimens 2117 are treated with the plasma generated. In FIG. 10, reference numeral 2106 indicates an exhaust pipe, reference numeral 2107 indicates a gas feed pipe, and reference numeral 2124 indicates cooling gas which is flown in the inside of the metallic antenna 2121. The above publication describes that according to the apparatus shown in FIG. 10, a plasma region of an area which is larger that the diameter of the waveguide 2102 can be formed in the space surrounding the antenna 2124, and the gas pressure of the plasma can be controlled to a large extent.
However, in the case of the plasma treating apparatus of the constitution shown in FIG. 10, the coaxial antenna is always positioned within the plasma generation chamber and because of this, a given inside area of the plasma generation chamber which is occupied by the coaxial antenna is not dedicated for the plasma treatment. Therefore, there is a limit for the capacity of the inside area of the plasma generation chamber which can be dedicated for the plasma treatment. Hence, this plasma treating apparatus hardly satisfies the requirement of establishing a high density plasma region of a large area as much as possible within a limited capacity so that the plasma can be efficiently utilized. In addition, the density of an electric power which can be applied to the coaxial antenna is governed by the size thereof and therefore, there is a restriction for the density of an electric power which can be applied to the coaxial antenna. In view of this, it is almost impossible for this plasma treating apparatus to attain high speed plasma treatment in which it is required to apply a microwave with a great electric power.
As an example of the apparatus in which the above manner (ii) is employed, there can be mentioned a plasma CVD apparatus of the constitution in which a microwave is introduced into a plasma generation chamber through a dielectric window which is described, for example, in Japanese Laid-open patent application No. 186849/1985.
The plasma CVD apparatus disclosed in said publication No. 186849/1985 is of the constitution shown in FIG. 11. The plasma CVD apparatus shown in FIG. 11 comprises a vacuum vessel as a deposition chamber 2222 in which a plurality of rotary shafts 2238 are spacedly arranged in parallel with each other, and a cylindrical drum member 2212 is positioned on each of said plurality of rotary shafts such that it can be rotated. The cylindrical drum members 2212 are rotated by a driving chain 2264 extending from a motor 2250. In FIG. 11, there are shown only two cylindrical drum members, but in practice, six cylindrical drum members 2212 are concentrically arranged while maintaining an equal interval between each adjacent cylindrical drum members to establish an inside chamber 2232 circumscribed by the six cylindrical drum members. The plasma CVD apparatus is hermetically provided with a microwave transmissive window 2296 which is situated above the inside chamber 2232. Reference numeral 2272 indicates a microwave power source. A microwave energy from the microwave power source is introduced into the inside chamber 2232 through an antenna probe 2276, waveguides 2280 and 2284, and the microwave transmissive window 2296. Similarly, the plasma CVD apparatus is hermetically provided with another microwave transmissive window 2294 which is situated below the inside chamber 2232. Reference numeral 2270 indicates another microwave power source. A microwave energy from this microwave power source is introduced into the inside chamber 2232 through an antenna probe 2274, waveguides 2278 and 2282, and the microwave transmissive window 2294.
The formation of a deposited film in this plasma CVD apparatus is conducted, for example, in the following manner. That is, the inside of the vacuum vessel 2222 is evacuated to a desired vacuum degree through an exhaust pipe 2224. Thereafter, raw material gases are introduced into the inside chamber 2232 through gas feed pipes 2226 and 2228. Microwave energy is then introduced into the inside chamber 2232 from the above and below sides, wherein the raw material gases introduced therein are decomposed to produce plasma 2268, whereby causing the formation of a semiconductor film for electrophotography on the surface of each of the cylindrical drum members 2212 each being maintained at a desired temperature by a heater 2200. The above publication describes that according to this plasma CVD apparatus, there can be formed a uniform deposited film on each of the cylindrical drum members 2212 at a high raw material gas utilization efficiency. However, in practice, there are disadvantages for the plasma CVD apparatus shown in FIG. 11 such that since the apparatus is of such constitution that microwave is introduced into the inside chamber 2232 from the above and below sides, the density of plasma generated in the vicinity of each of the microwave transmissive windows 2296 and 2294 unavoidably becomes higher than the density of plasma generated at the central part of the inside chamber 2232 and because of this, it is extremely difficult to form a uniform plasma region with a uniform density in the space of the inside chamber 2232, and as a result, the resulting deposited film on each of the cylindrical drum members 2212 varies in terms of film property between the film deposited on each of the opposite end portions of the cylindrical drum member 2212 and the film deposited on the central portion thereof. The plasma CVD apparatus shown in FIG. 11 also has a disadvantage such that since a microwave is introduced through each of the opposite microwave transmissive windows 2296 and 2294, it is necessary to appropriately adjust the microwave propagation mode and the position of each of the opposite waveguides such that the microwave introduced through one of the opposite microwave transmissive windows is prevented from transmitting through the other microwave transmissive window to get into the waveguide and the microwave power source.
As an example of the apparatus in which the above manner (iii) is employed, there can be mentioned a plasma treating apparatus of the constitution in which a microwave is introduced into a plasma generation chamber through slots (that is apertures) disposed at a waveguide which is described, for example, in Japanese Laid-open patent application No. 30420/1991. The plasma CVD apparatus described in this publication comprises a film-forming chamber (that is, a plasma generation chamber) having a circumferential wall formed by curving a web member as said web member is continuously moving in the longitudinal direction, in which a deposited film is formed on the inner wall face of the film-forming chamber. FIG. 12 is a schematic explanatory view illustrating the configuration of a circular waveguide 2301 which is used for introducing a microwave into the film-forming chamber of the plasma CVD apparatus. The circular waveguide 2301 has an end portion 2303 and a plurality of slots (that is, apertures) 2304 to 2308 being spacedly formed through one side thereof. A microwave transmitted from the direction expressed by an arrow is introduced into the film-forming chamber through the slots 2304 to 2308. The above publication describes that according to this plasma CVD apparatus, it is possible to continuously and uniformly form a large area of deposited film, and the thickness of the deposited film formed can be properly controlled by adjusting the transportation speed of the web member. However, there are disadvantages for this plasma CVD apparatus such that the density of plasma generated in the vicinity of the slots disposed at the waveguide 2301 in the film-forming chamber is remarkably higher than that of plasma generated in other regions in the film-forming chamber and because of this, it is extremely difficult to produce plasma in a uniform state in the film-forming chamber, and therefore, a well-skilled technique is required in order to form a homogenous and uniform deposited film on a large area web member. Incidentally, the circular waveguide 2301 is of the constitution in that the end portion 2303 is provided to terminate propagation of the microwave.